This invention relates to integrated circuits, and more particularly, to charge pump circuitry for integrated circuits.
Charge pumps are widely used in integrated circuits. For example, charge pump circuits may be used to generate a negative body bias voltage to apply to the p-wells of n-channel metal-oxide-semiconductor transistors on an integrated circuit to reduce leakage current and power consumption. The use of a charge pump may make it possible to produce a bias voltage of a magnitude or polarity that might otherwise be difficult to supply using an external pin.
Charge pumps use oscillators to produce a charge pump clock signal. The charge pump clock signal is applied to each of the stages of the charge pump. When the clock signal in a charge pump is active, the charge pump will produce its desired output voltage at an output terminal.
In circuits in which a voltage of a particular value is needed, charge pump circuits may be regulated using feedback. For example, a comparator may compare the output voltage on the output terminal of the charge pump to a reference voltage. The oscillator for the charge pump can be turned on and off in response to the output of the comparator as needed to adjust the output voltage.
To provide sufficient current handling capability, a typical integrated circuit may have a number of charge pumps whose outputs are connected in parallel. The charge pumps may be distributed around the integrated circuit so that the output voltage can be delivered where needed. A charge pump circuit that is formed from multiple smaller charge pumps in this way will be able to operate properly under a variety of load conditions.
The number of charge pumps that are connected in parallel in a given design is based on a worst-case scenario. A designer takes into account the worst possible set of manufacturing and operating variables (e.g., temperature, oxide thickness variations, etc.). Based on this worst-case scenario, the designer determines how many charge pumps should be included in the charge pump circuit. To ensure proper operation under all conditions, the charge pump circuitry tends to be over-designed (i.e., there are more charge pumps in the circuit than are necessary in most normal operating situations).
While over-designing charge pump circuitry in this way ensures that the charge pump circuitry will have sufficient capacity to handle its load, the inclusion of multiple charge pumps that operate in parallel can lead to ripple. This is because conventional charge pump circuits that include multiple charge pumps connected in parallel turn all of the charge pumps off and on at the same time. Excessive ripple gives rise to undesired noise that can adversely affect device performance.
It would therefore be desirable to be able to provide improved charge pump circuitry for use on integrated circuits.